The present invention generally relates to a system for positioning a grappler relative to a container to be lifted and more particular relates to a system for aiding in the guidance of the grappler so that twistlock mechanisms of the grappler may be precisely aligned with locking holes of a container.
Gantry cranes are conventionally used in railyards, shipping yards, and other places for loading and unloading large containers to and from railcars, trailers, pallets, etc. Such a crane typically has a sturdy steel frame with four vertical columns, upper horizontal beams fixed between the columns, and a lifting mechanism movably mounted to the beams. The lifting mechanism has twistlocks or spreader clamps to lockably engage the container in a standard manner.
The grappler is movably suspended from the frame so that the grappler can be positioned and lowered to engage a container. More specifically, the lifting mechanism generally includes a trolley traversibly mounted on the horizontal beams for side-to-side movement. Also, the grappler is suspended from the trolley by cables or wire ropes or other means. On some cranes, the suspended grappler may be moved forwardly or rearwardly along the trolley as well. Additionally, the hoisting means are operably movable to selectively lift and lower the grappler.
The grappler must be properly positioned and lowered to engage a container to be lifted. Specifically, the grappler must be carefully landed on top of the container while aligning the four grappler twistlocks with the four respective corner-located locking holes in the container.
Properly landing the grappler on a container with precise alignment in this manner has conventionally been difficult. A gantry crane conventionally has a cab which is mounted to the frame and which contains controls for driving the crane and positioning the grappler. Conventionally, the operator controls the grappler by eyesight from a vantagepoint through the cab window. Accordingly, the operator has been typically required to maneuver and lower the grappler to land on top of a container with precise positioning.
Such manual "eyeball" positioning can be difficult, especially when the grappler is moved to a distal position relative to the cab. The operator's ability to align the conventional grappler in such a manner requires keen depth perception, concentration and alertness. Extra personnel are sometimes required to stand near the container and provide hand signals to assist the operator. Additionally, changes in lighting and weather conditions may impede an operator's ability to accurately position the grappler.
Various positioning aids have been attempted in the art. For example, U.S. Pat. No. 5,067,013 discloses a crane having two video cameras mounted at opposite corners of a grappler. The cameras are directed downwardly toward a container to be engaged. The video signals from the cameras are displayed on monitors in the cab to assist the crane operator in positioning the grappler.